AbstractEvidence is presented that singlet oxygen may have an important role in the photo‐oxidation of polymers. Increased attention is being paid to singlet oxygen as a possible reactive intermediate in the initiation step of the photodegradation of polymers. Singlet oxygen may be produced by energy transfer either from impurities or internal groups after excitation, e.g. carbonyl groups, which are present in commercial polymers. As a consequence, reactions of singlet oxygen may also be important in the stabilization of polymers, e.g. leading to search for new and more effective antioxidant